Single deck contact type floating roof



y May 12, 1959 F.. D. MQYER ET AL SINGLE DECK CONTACT TYPE FLOATING ROOFFiled Oct. 12, 1954 4 Sheets-Sheet l Zeig l 75 //5 www: E W2 il .ZYZ' Q-f ,ZV/Zevg;

May 12, 1959 F. D. MOYR ET AL 2,885,204

SINGLE DECK c-oNTAcT TYPE FLOATING ROOF Filed oct. 1 2, 1954 v 4sheets-Sheet 2 May 12, 1959 Filed oct. 12.- 1954 F. D. MOYER ET Al.2,886,204

SINGLE DECK CONTACT TYPE FLOATINC ROOF 4 Sheets-Sheet 3 l Egg,

ZU Z6 May 12, 1959 -F. D. MOYER ETAAL v 2,886,204

SINGLE DECK CONTACT TYPE FLOATING ROOF Filed Oct. l2, 1954 4Sheets-Sheet 4 Ain Figure 7 (stitfeners omitted) ;l

United, States Patenfolf SINGLE DECK coNTAcr TYPE ELoATrNG RoorFrederick D. Moyer, Chicago, and Clilford M.-rr, Western Springs, Ill.,assignors to Chicago Bridge & Iron Company, a corporation of IllinoisApplication October 12, 1954, SeralNo. 461,718

s claims. (nizza-26) This invention relates to a tank floating roofofthe single deck contact type.

In such a roof, the contour of the lower face of the deck, whichundernormal floating conditions is entirely in contact with the liquid uponwhich it oats, is the same as the upper drainage area orjsurface ofthedeck, the upper and'lower faces being separated onlyl by the thicknessof the deck plates. y

One of the main problems with such a roof is drainage of surfacerainfall. In order to have adequate drainage it is important to have`appropriate slope or pitch, but the pitch of the roof is limitedspecifically bythe Weight of the roof and the specic gravity o 'f anygiven liquid on which it'oats. This is because more liquid is displacedas the slope increases and with any given roof weight and any Igivenspecific gravity of liquid, the entire under surface of the roof cannolonger be immersed in the-liquid when the slope has been increasedl toan eicient pitch.v y v l f.

It has been suggested in the past that-heavyweights be concentrated ator fnear the .center ofthe roof so that .it canv be further immersed,but this adds ymore problems than it solves. y,

In the present invention the problem is solved', without the addition ofunnecessary weight, by providing steps in vertical cross section toprovide a pluralityof integrated drainage areas, the steepness of the'slope in at least one of such areas, and preferably in all,substantially exceeding the steepness of the slope possible with asingle drainagearea on a roof of the same size and weight.

In one form of the invention the drainage areas comprise a plurality ofconcentric annuli, with drains connecting the ring drainage area formedat the junctions of the annuli with a central drainage area. l a

In another form of the invention the drainage areas are radial,comprising radial wedges sloped to provide radial vdrainage areasbetween them.

It is also possible to'coinbine these forms of drainage areas. f v

The invention is illustrated in the drawings, in which:

Figure l is a partial plan Vview of one form of the roof (stifeners ortrusses omitted);

Figure 2 is a vertical vsection taken .along the line 2--2 in Figure 1(stieners or ytrusses omitted);

Figure 3 is a vertical section taken along the line 3-3 in Figure l(stiEeners or truss'es'omitted);

'Figure 4 is a developed vertical cylindrical section taken along theline 4--4 in-Figure l;

lFigure 5 is a partial plan view of a modified form of 'ure 5;

Figure 7 is a partial plan view of a modified form of the invention;

Figure 8 is a vertical section taken along the line ,t5- 8 2,886,204 yfffifel Mer, 12, 1,959

. 2 i Figure 9Vv is a partial plan View of aimodiiied form'of theinvention; "v

Figure 10 is a'section taken along the line 10--10 m Figure/9(stiifeners omitted); A i' Figure 11 is ay partial plan view-of anotherformof the invention (stiffeners included); and"l Q Figure 12 is asection taken along the line f12-12'in Figure 11. 'i i f The4 firstsuccessful'oating roofs were of the pan .or pontoon-less type. This is`the most economical type of vfloating roof and is widely Vusedtoday'for crude oils and products o f "relatively low volatility whichyrequire reduction of lling losses, prevention of corrosionl from sour'liquids and protectionagainst losses from fire,` but do not require theadditional insulation of a pontoon lor double deck type of roof.

Such a roof must be of the fcontact type-'-that is', it must float withthe entire underside of the roof wetted by the stored product, iflcorrosion of the roof is to be reduced to the minimum. It must falso bepitched for drainage of rain water vbecause the roof, having nostabilizing pontoons, is subject to tipping and even'sinking if alargevv quantity of water vis `allowedfto collecton the deck.

In the past mostpan roofs were .built withwthe singleof water, and sincethis simplest type of roof was rela-- tively light comparedy withpontoon-type ondouble-deckftypewroofs, the slope of 'the cone even whenshaped'by the mentioned trusses, was .nevertheless quite .fiat andydrainage of rain water was not always satisfactory.

Structurally, ther-,conical shape -Wasfar from ideaLyfor the heavy outerportion Vof the roof displaced ,much less than its weight while thecentral portion displaced more than its weight thus creating atendencyfor. the center of the roof to -be displaced upwards comparedwith the outer portion, destroying adequate drainage. Thefioof,therefore, had to be held in this conical shape by heavy trusses.` f lAs an example, ythe slopefrom rim `to center` for-a roof in a tank 140feet in diameter vmight be' about 7inche`s, and the drainage pitch thusonly 7 inches in approximately feet, or one-'inch Sin approximately 10feet. Roofs usually were built ofv lap-jointed plates of 5716 Vinchthickness which, without ,any 'trussing or supports, weighed about 8pounds per square foot and'thus tended to displacelmore than 1% inchesof'aproduct weighing 54 pounds per cubic foot. Sincetthe slope of theconical deck was about one' inch in 10 feet, the weight of steel wasgreater than the'theoretical displacement for' an outer annular:portionxof the deck nearly 18 feet wide, and this portion tended'to sagbetween trusses. Furthermore, a large portion ofthe weight of a pan roofwas made up of the devices used to .seal'the space between theouter rimof 'the roof and'the tank shell, and the outer rim itself was a'heavyplate, .so thetrusses had to lift these outer loads,includingthe'weightof the outer deck plates not balanced bydisplacement, land transfer them toward the center yof the roof wherethe displacement exceeded the weight.

The result was that not only did the roof drain lpoorly because ofinsuicient pitch and the other reasons listed, but also the `trussingprovided for forcing the 'roof finto shapehad to be designed forlargeloads.

vTherewere'other disadvantages vof* :the old design.

When a tankwas emptied, the roof could not be allowed to come to restdirectly on the tank bottom because it was not the 4same shape asthegbottom, and'further because a drain pipe andother devices beneaththey roof required clearance. Therefore, it was necessary to provide astructure forlanding the roof in its low position; and since -thissupporting structure carried not only the weight of the roof butlalsothe weight of water, snow and ice that accumulated while the roofwas landed, it was a heavy and costly structure. Usually'it consisted ofa large number of individual leg supports, the large number beingrequired becausecach leg was connected only to. thesingle-thickness deckplates andthe load per support waslimitedlby the strength of the deckplates and the firmness ofthe grade on which the deck plates rested.

Another disadvantage of theoriginal design of pan floating 'roof was thediliiculty of assembling .and joining the deck plates. Neither thetrusses nor the supports, alone or in combination, could be used forsupporting the -individual deck plates when `the roof was being built.The trusses were too widely spaced to hold the plates lin properl shape,and the leg supports tended to distort the unstitfened deck plates nearthe supports.

` The present floating roof design has the following advantages: f y

(1) Improved drainage with positive radial or circumferential pitch orboth radial and circumferential pitch toward the sump.

(2) Improved `trussing with adequate circumferential as well as radialframing.'

(3) Reduced bending moments due to improved location of buoyancy withrespect to weight. This is partially responsible for the reduction inthe cost of trussing.

(4) Reduced erectioncost due to elimination of heavy temporary supportsfor construction.

(5) In some cases a smaller number of adjustable supports and morepositive load distribution on supports resulting from use ofcircumferential framing.

It is contemplated that the high portions formed by the steps be ventedsince'it is not normally desired to collect gas in these high spots. Theform of vents, however, is no part of the present invention.

l In Figures l, 2, 3 `ancl 4 the wedge-shaped stepping is illustrated.

`As there shown, a floating roof is divided into a number of pie-shapedwedges or segments 11. l These are .divided alternatelylby ridges`12.and valleys 13. In this form of the invention the drainage areas aregenerally warped having constantly changing pitch and all of thevdrainage follows the valleys; 13 to the central sump 14 from which adrain 15 leads to the bottom of the tank.

.In Figures 5 and 6, a form of the invention in which a plurality ofannuli is used is illustrated. In this form the single deck portion isdivided into an outer annulus and an inner annulus 21 .separated by thestep 22.

Adrain trough 23 Vconnects the lowermost portion of the `tions'oftheroof to the :sump do not a'dd significantly to the displacement ofliquid.

In Figures 7 and 8, .a modified form is shown in which a pon-toon 25 isprovided in combination with a single deck of the contact type havingannuli 20 and 21. Sim- `ilarly, ysingle decks of the contact type asshown in the other figures may be combined with a pontoon.

Figures 9 and `10 illustrate a combination form in .which thesingle1deckportion comprises a central con- CII ical portion 30, whichmay be considered as an annulus surrounding and sloping inwardly ltowardthe sump 14 and the radial segments 32 which in combination with eachother form alternate ridges 33 and valleys 34. Drainage of the radialsegments 32 is to the ring drainage area 31 which is connected by aseries of troughs 35 to the central sump. f f i Figures l1, and l2 aredetailed fragmentary views i1- lustrating another form of the inventionhaving three anular areas 60, 61 and 62.separated by steps 63, 64 and65. Drainage is to the central sump 66. Y

Trussing is accomplished by means of the rafters 70, 71 andL 72 andposts73,*74 and 75. These are connected by conventional rods 76, 77, 78 and79. Similar trussing may be provided in the other forms of the inventionthough not shown.

In the particular form illustrated in Figures l1 and l2, the annuli 60and 61 are 20 feet wide; the annulus 62 is 25 feet wide; and the sump is4 feet in radius. This roof will accommodate a foot tank.

The outer annulus 60 has pitch of 5 inches; annulus 61 has a pitch of 5inches; and annulus 62 has a pitch of 7 inches. All of these are steeperthan the pitch that could be accomplished by using a single cone of thesame size and weight oating on the same liquid and in contact therewithand could be increased further by adding the ridge and valleyconstruction shown in Figures l, 2, 3, 4, 8, 9 and 10.

The above detailed description has been given for clearness ofunderstanding only and no unnecessary limitations should be understoodtherefrom as modifications will be obvious to those skilled in the art.

We claim:

l. A oating roof of the contact type for a liquid storage tankcomprising a single roof deck `portion to cover liquid in the tank, thelower surface of the roof deck being adapted to remain substantiallycompletely incontact with the liquid in the tank, said roof deck havingportions sloped transversely to a radius of the roof and portions slopedradially toward the center of the roof to divide the upper surfacethereof into drainage areas converging toward the center of the roof,said drainage areas comprising a plurality of concentric annuli formingat least one ring-like drainage trough, a central outlet to receive thedrainage from the converging drainage areas, a communicating passagefrom said trough to said central drainage outlet, said communicatingpassage being adapted to permit gravity flow of surface liquid from saidtrough to said outlet, the total eiective slope of each drainage areaexceeding the maximum slope possible in a continuous single deck roof ofsubstantially the same weight and size having its lower surfacemaintained substantially in contact with the liquid in the tank.

2. A oating roof `of the contact type for a liquid storage tankcomprising a single roof deck portion to cover liquid in the tank, thelower surface of the roof deck being adapted to remain substantiallycompletely in contact with the liquid in the tank, said roof deck havingportions sloped transversely to a radius of the roof and portions slopedradially toward the center of the roof to divide the upper surfacethereof into drainage areas converging toward the center of the roof,said drainage areas comprising a plurality of concentric annuli formingat least one ring-like drainage trough, a central outlet to receive thedrainage from the converging drainage areas,

size having its lower surface maintained substantially in contact withthe liquid in the tank.

3. A oating roof of the contact type for a liquid storage tankcomprising a single roof deck portion to cover` liquid in the tank, thelower surface of the roof deck being adapted to remain substantiallycompletely in contact with the liquid in the tank, said roof deck havingportions adapted to be drained in directions transverse to a radius ofthe roof and portions adapted to be drained along radii toward thecenter of the roof to divide the upper surface thereof into drainageareas converging toward the center of the roof, said drainage areascomprising a plurality of concentric annuli forming at least onering-like drainage trough, a central outlet to receive the drainage fromthe converging drainage areas, a communicating passage from said troughto said central drainage outlet, said communicating passage beingadapted to permit gravity flow of surface liquid from said trough tosaid outlet, the total effective slope of each drainage area exceedingthe maximum slope possible in a continuous single deck roof ofsubstantially the same Weight and size having its lower surfacemaintained substantially in contact with the liquid in the tank.

4. A oating roof of the contact type for a liquid storage tankcomprising a single roof deck portion to cover liquid in the tank, thelower surface of the roof deck being adapted to remain substantiallycompletely in contact with the liquid in the tank, said roof deck havinga plurality of concentric annular drainage troughs With the outerperiphery of one adjacent to the inner periphery of the other, the outerannular trough being adapted to drain toward the roof center and to havethe accumulation then drain transversely to a radius of the roof andturn downwardly toward the inner annular trough, said inner troughhaving portions sloped radially toward the center of the roof to dividethe upper surface thereof into drainage areas converging toward thecenter of the roof, a central outlet to receive the drainage from theconverging drainage areas, a communicating passage leading from theinner annular trough to said drainage outlet, the flow from each annulartrough being gravitational to provide a final drainage of the roof atits center, the total effective slope of each drainage area exceedingthe maximum. slope possible in a continuous single deck roof ofsubstantially the same weight and size having its lower surfacemaintained substantially in contact with the liquid in the tank.

5. The lloating roof claimed in claim 4 comprising in addition agenerally annularly shaped pontoon positioned in contact with the outerannular trough and having its inner periphery in engagement with theouter periphery of the outer trough.

References Cited in the le of this patent UNITED STATES PATENTS1,886,131 Smith Nov. 1, 1932 2,282,772 Wiggins May 12, 1942 2,321,058Wiggins .Tune 8, 1943 2,359,416 Hammeren Oct. 3, 1944 2,464,786 AllenMar. 22, 1949 2,538,033 Orr Jan. 16, 1951 2,664,220 Cord et al. Dec. 29,1953 2,750,067 Wiggins June 12, 1956

